1. Field of the Invention
The present invention is directed to the field of flying electrical generators (FEGs) and, more particularly, to new configurations of Flying Electric Generators (FEGs) featuring rotors positioned on a frame or body such that each rotor receives clean air which is undisturbed by the other rotors mounted to the frame or body.
2. Brief Description of the Related Art
Flying Electric Generators are not new and several methods of extracting energy from high altitude winds have been proposed and are now in development. It is well known that the energy content in wind increases with distance from the ground (altitude). Current ground based wind turbine technologies attempt to take advantage of this fact by mounting wind driven rotors at greater heights and by extending blades to greater lengths. However, due to the cantilever design of ground based wind driven generators, there is a limit to their maximum height, as large and costly steel and concrete bases are required to counter the bending forces introduced by their necessary structural geometry. FEGs, in contrast, need only a thin, light tether attached to a small ground anchor point to counter or react to the force of the wind, and they can fly high above the ground and into the most concentrated and abundant natural energy source, the high altitude winds.
Currently, and as shown in FIGS. 1 and 2, autogyro rotor based FEGs, 10, 10′, respectively, in development have at least four rotors, with two rotors 11, 11′ and 13, 13′ rotating in one direction, and two rotors 12, 12′ and 14, 14′ rotating in the other direction. The most commonly seen configuration includes four rotors mounted in a symmetric square pattern to an X-shaped frame or fuselage 15, as shown in FIG. 1, or to an H-shaped frame or fuselage, as shown in FIG. 2. Other symmetric configurations have been studied, including those with larger numbers of rotors with even numbers of sets of counter rotating pairs of rotors. For example, as shown in FIG. 3, an eight rotor FEG could have four rotors 16A-16D clustered in a square pattern, with four more rotors 17A-17D in another square pattern positioned 45 degrees to the rotors 16A-16D. As shown, the rotors which are diagonally positioned relative to one another in each square have blades rotating in one direction which is opposite that of the two other diagonally positioned rotors in each square. This configuration would be suitable for a hovering platform multi-rotor helicopter, but symmetrically spaced rotors create problems for FEG applications.
During flight of prior art FEGs, when an angle of attack of the rotors is at a relatively small angle, see the discussion below with respect to the angle of attack with respect to the FEGs of the present invention and shown in FIGS. 4 and 5, the downward component of the air flow emerging downwind of each forward rotor causes a reduction in thrust of an aft rotor directly downwind. This is because the downward component of flow behind the forward rotor changes the apparent wind direction for the aft rotor. The apparent wind experienced by an aft rotor downwind of a forward rotor has a downward component, which is equivalent to a relative reduction in pitch angle for that aft rotor. Reduction of pitch angle reduces thrust. The result of the loss of thrust in an aft rotor is a rapid and uncontrolled increase in vehicle pitch. During testing, this interaction was discovered and the present invention has been made to eliminate this problem.
The foregoing problem disappears when an angle of attack becomes large, but the problem area, flight in wind with taught tether at low positive pitch angles, must be traversed to achieve the larger angle of attack. At large positive angles of attack, the forward rotors are so far above the aft and downwind rotors that the downward-directed flow trailing the forward rotor does not always reach the aft rotor, and it operates in somewhat undisturbed air.